Lead motion sensing via cable microphonics

ABSTRACT

An ambulatory medical device can include an excitation circuit configured to be electrically coupled to an implantable lead, the excitation circuit configured to provide a non-tissue-stimulating first signal to the implantable lead when the implantable lead is located at or near a tissue site. In an example, the system can include a detection circuit configured to be electrically coupled to the implantable lead and configured to receive a second signal, in response to the first signal, from the implantable lead, the second signal is determined at least in part by a motion of the implantable lead.

CLAIM OF PRIORITY

This patent application claims the benefit of priority, under 35 U.S.C. Section 119(c), to Ingle, U.S. Provisional Patent Application Ser. No. 61/359,430, entitled “LEAD MOTION SENSING VIA CABLE MICROPHONICS,” filed on Jun. 29, 2010 (Attorney Docket No. 279.I30PRV), which is hereby incorporated by reference herein in its entirety.

BACKGROUND

A beating heart can vibrate, such as during the opening or closing of the heart's valves. In some cases, the vibrations that result from the valve closings can be detectable, such as providing an audible indication or a detectable mechanical vibration. Such vibration can also be indicative of one or more other events. Blood flow through blood vessels can also produce detectable mechanical vibrations, such as including one or more distinct sounds. Detection of cardiac or vascular mechanical vibrations can provide information useful in assessing or diagnosing various medical conditions. Such detected mechanical information can be used by an implantable or ambulatory medical device to adjust patient therapy, to diagnose or monitor one or more physiologic conditions, or such information can be stored such as for analysis by a caregiver.

Cardiac electrotherapy devices can include electrode leads, such as for delivering electrical energy to particular cardiac regions. Some electrode leads can be elastic and deformable, such as in response to heart muscle contractions. Ferek-Petrie, in U.S. Pat. No. 5,693,074, entitled “CARDIAC ELECTROTHERAPY DEVICE FOR CARDIAC CONTRACTION MEASUREMENT,” refers to leads with multiple conductors that can transmit high frequency signals. Samuelson et al., in U.S. Pat. No. 5,361,776, entitled “TIME DOMAIN REFLECTOMETER IMPEDANCE SENSOR METHOD OF USE AND IMPLANTABLE CARDIAC STIMULATOR USING SAME,” refers to a time domain reflectometry impedance sensor for measuring body impedance along a lead.

OVERVIEW

Generally, a healthy heart can provide at least two distinct heart sounds. The first sound, “S1,” is typically produced by the closing of the atrioventricular valve leaflets. The second sound, “S2,” is typically produced by the closing of the semilunar valve leaflets. In a clinical setting, these events can be detected such as through cardiac auscultation by an examiner, using a stethoscope.

In some individuals, various cardiac conditions can cause additional detectable mechanical vibrations, though these may or may not be audible to the examiner. For example, a heart murmur can occur when blood is flowing harder or faster than in an otherwise healthy individual. Such a murmur can indicate a serious heart problem or merely a benign cardiac event. In another example, an “S3” sound, also known as a protodiastolic gallop, can indicate a failing left ventricle. An “S4” sound, also known as presystolic gallop, can sometimes be detected in patients exhibiting restrictive cardiomyopathy.

In addition to vibrations or sounds indicative of heart function, blood flowing through blood vessels can also produce detectable vibrations useful for diagnosis and assessment of various medical conditions. The location, velocity, and pressure of blood flow are variables that can be assessed by detection of such vibration, among other variables. Thus, mechanical vibration monitoring capabilities can be included in an implantable or an ambulatory medical device, such as to store such information for later review or analysis, or to respond to such mechanical information. For example, an individual with an implantable medical device, such as a pacemaker, can benefit from mechanical vibration monitoring, including heart sound monitoring. Such monitoring can be used for diagnosis, or an initiation or adjustment of treatment. By identifying a mechanical vibration (e.g., including one or more heart sounds), therapy can be tailored to an individual's needs, or heart sound abnormalities can be provided to a caregiver for assessment or treatment.

Implantable acoustic and mechanical transducers can be used in detecting heart and blood mechanical vibrations (e.g., including one or more heart sounds). However, the resulting acoustic information from these transducers can produce a low signal level that can be degraded by extraneous noise. Furthermore, devices having a dedicated acoustic or mechanical transducer can require additional sensors within, on, or attached to the implantable or ambulatory device, such as resulting in a greater surface area, physical volume, or number of interconnects as compared to a comparable implantable device lacking such a dedicated acoustic or mechanical transducer.

The present inventor has recognized, among other things, that mechanical information indicative of cardiac, blood, or vascular motion can be detected using a motion of one or more conductors electrically coupled to the ambulatory or implantable device. For example, the present inventors have also recognized that an implantable lead electrically and mechanically tethered to an implantable or ambulatory medical device can provide information indicative of the motion of the lead, such as using one or more electrical measurements as described in the following examples, such as to detect cardiac, blood, or vascular motion. Such information indicative of motion can also be used to time or to verify the effectiveness of a cardiac therapy (e.g., electrostimulation), in addition to diagnosing one or more cardiac conditions.

An ambulatory medical device can include an excitation circuit configured to be electrically coupled to an implantable lead, the excitation circuit configured to provide a non-tissue-stimulating first signal to the implantable lead when the implantable lead is located at or near a tissue site. In an example, the system can include a detection circuit configured to be electrically coupled to the implantable lead and configured to receive a second signal, in response to the first signal, from the implantable lead, the second signal determined at least in part by a motion of the implantable lead.

This overview is intended to provide an overview of subject matter of the present patent application. It is not intended to provide an exclusive or exhaustive explanation of the invention. The detailed description is included to provide further information about the present patent application.

BRIEF DESCRIPTION OF THE DRAWINGS

In the drawings, which are not necessarily drawn to scale, like numerals may describe similar components in different views. Like numerals having different letter suffixes may represent different instances of similar components. The drawings illustrate generally, by way of example, but not by way of limitation, various embodiments discussed in the present document.

FIG. 1 illustrates generally an example of a system comprising an ambulatory medical device that can include an excitation circuit, a detection circuit, a coupling to an implantable lead, a signal processor, or an output.

FIG. 2 illustrates generally an example of a portion of a system that can include an implantable medical device, an implantable lead, or a communicative coupling between the implantable medical device and an external assembly.

FIG. 3 illustrates generally an example of a portion of a system comprising an excitation circuit that can include an oscillator circuit, a detection circuit, a coupling to an implantable lead, a signal processor circuit, or an output.

FIG. 4 illustrates generally an example of a portion of a system comprising an excitation circuit that can include an oscillator circuit, a detection circuit comprising a coupling to an implantable lead and a bridge circuit, a signal processor circuit, or an output.

FIG. 5 illustrates generally an example of a portion of a system that can include an excitation circuit such as including a pulse generator circuit, a detection circuit including a coupling to an implantable lead and a voltage detector, a signal processor circuit, or an output.

FIG. 6 illustrates generally an example that can include providing a first signal, receiving a second signal, or extracting information indicative of lead motion from the second signal.

FIG. 7 illustrates generally an example that can include generating an oscillating first signal, providing the first signal to an implantable lead, receiving a second signal from the implantable lead, demodulating the second signal, or extracting information indicative of lead motion from the second signal.

FIG. 8 illustrates generally an example of a portion of a method such as including generating an oscillating first signal, providing the first signal to an implantable lead, receiving a second signal from the implantable lead, receiving a voltage, or extracting information indicative of lead motion from the received voltage.

FIG. 9 illustrates generally an example that can include generating a pulsed first signal, providing the first signal to an implantable lead, receiving a voltage, or extracting information indicative of lead motion from the received voltage.

FIG. 10 illustrates generally an example that can include generating a pulsed first signal, providing the first signal to a first capacitance, providing the first signal to a second capacitance, receiving a first voltage, receiving a second voltage, or extracting information indicative of lead motion from the received first and second voltages.

DETAILED DESCRIPTION

The following detailed description includes references to the accompanying drawings, which form a part of the detailed description. The drawings show, by way of illustration, specific embodiments in which the invention may be practiced. These embodiments, which are also referred to herein as “examples,” are described in enough detail to enable those skilled in the art to practice the invention. The embodiments may be combined, other embodiments may be utilized, or structural, logical and electrical changes may be made without departing from the scope of the present invention. The following detailed description is, therefore, not to be taken in a limiting sense, and the scope of the present invention is defined by the appended claims and their equivalents.

In this document, the terms “a” or “an” are used, as is common in patent documents, to include one or more than one. In this document, the term “or” is used to refer to a nonexclusive or, unless otherwise indicated. Furthermore, all publications, patents, and patent documents referred to in this document are incorporated by reference herein in their entirety, as though individually incorporated by reference. In the event of inconsistent usages between this document and those documents so incorporated by reference, the usage in the incorporated reference(s) should be considered supplementary to that of this document; for irreconcilable inconsistencies, the usage in this document controls.

FIG. 1 is a diagram illustrating generally an example of a system 100 comprising an ambulatory medical device 105 that can include an excitation circuit 110, a detection circuit 120, a signal processor 130, an output 140, an interconnect 160, or a lead coupling 170. In an example, an implantable lead 150 can be coupled to the lead coupling 170. One or more of the excitation circuit 110, detection circuit 120, signal processor 130, output 140, or interconnect 160 can be realized on or within a commonly shared substrate, such as on a commonly-shared integrated circuit, module, circuit board, or the like. In another example, each block can be included in a physically separate ambulatory device, such devices coupled as shown in the example of FIG. 1, such as using one or more wired or wireless communicative couplings.

In the example of FIG. 1, the ambulatory medical device 105 can include a cardiac stimulator, such as including pacing or cardiac resynchronization therapy (CRT) circuitry configured to deliver pacing or resynchronization energies to cardiac tissue. In an example, the ambulatory medical device 105 can include a neural stimulator device, such as to provide electrical, mechanical, optical, acoustic or chemical stimulation to one or more neural targets.

In the example of FIG. 1, the excitation circuit 110 can be coupled to a detection circuit 120. The excitation circuit 110 generally provides an excitation energy, such as including a first signal. In an example, the first signal can include an oscillating electrical signal, such as a time-varying voltage or current. In an example, the first signal can include a pulsed electrical signal, such as including one or more current or voltage pulses including a specified amplitude, duration, pulse repetition rate, duty cycle, or morphology, among other parameters. In an example, the excitation circuit 110 can be coupled to the lead coupling 170 via interconnect 160, such as using a header or other connector included as a portion, part, or component of the medical device 105.

In the example of FIG. 1, an implantable lead 150 can be coupled to the lead coupling 170. For example, the implantable lead 150 can include one or more conductors. In an example, the implantable lead 150, such as coupled to the implantable lead coupling 170, can be located at a site within or on the body (e.g., including one or more surface, subcutaneous, or intravascularly-located electrodes or conductors). In an example, the implantable lead 150 can be implanted or otherwise place within a body, such as within or near a heart, either temporarily or more permanently, such as for ambulatory monitoring or therapy delivery.

In the example of FIG. 1, the detection circuit 120 can be coupled both to a signal processor 130 and the lead coupling 170 via a commonly-shared interconnect 160. In an example, the implantable lead 150, or an external lead, can be coupled to the lead coupling 170. In an example, the detection circuit 120 can be configured to receive a second signal provided by the implantable lead 150. For example, the detection circuit 120 can be configured to interpret or processes the first signal, such as by providing the first signal to the implantable lead 150 before or during receiving the second signal.

In the example of FIG. 1, the detection circuit 120 can be configured to receive a second signal, such as from the implantable lead 150 via the lead coupling 170 and the interconnect 160 (e.g., in response to the first signal). In au example, the detection circuit 120 can be configured to interpret and process a received second signal before transmitting the received second signal to the signal processor 130. For example, the detection circuit 120 can be configured to determine a first characteristic of the second signal (e.g., information about an amplitude, frequency, noise floor, signal-to-noise ratio, or one or more other characteristics). In an example, the amplitude characteristic of the second signal can be compared to a threshold value, and the result of the comparison can be used to determine if the received second signal can be further processed by the signal processor 130. For example, if the amplitude of the second signal meets or exceeds a threshold value, the detection circuit 120 can be configured to transmit the second signal to the signal processor 130 for further analysis. Conversely, if the amplitude of the second signal is below the threshold value, the detection circuit can withhold transmission of the second signal or otherwise indicate to the signal processor 130 that further analysis should be withheld (e.g., if the second signal is so low in amplitude that extraction of motion information would be difficult).

In the example of FIG. 1, the signal processor 130 can be coupled to the detection circuit 120 and the output 140. In an example, the signal processor 130 can be configured to receive information derived from the second signal. The signal processor 130 can be configured to extract from the second signal information indicative of motion of the implantable lead 150. Such motion of the implantable lead 150 can include a physical displacement of any constituent element of implantable lead 150 with respect to an equilibrium position. In an illustrative example, the implantable lead 150 can experience a physical displacement because the implantable lead is mechanically coupled to a vibrating tissue, such as implanted within or near contractile tissue in the heart. In an example, the information indicative of motion of the implantable lead 150 can include audible or acoustic information such as provided by a heart sound, or other higher or lower-frequency mechanical information not necessarily within the audible frequency spectrum. In an example, information indicative of motion of the implantable lead 150 can include impedance information, such as including a change in lead impedance determined at least in part by mechanically coupling cardiac or vascular mechanical vibrations to the implantable lead 150. For example, impedance information can be interpreted by the signal processor 130 to detect, classify, or monitor one or more physiological events. Such physiological events can include the closing of the atrioventricular or semilunar valve leaflets in the heart.

In the example of FIG. 1, the output 140 can be coupled to the signal processor 130. In an example, the output 140 can receive information from the signal processor 130. The received information can be passed through an output 140 to one or more other portions, parts or components of the ambulatory medical device 105. In an example, the output 140 can be coupled to another device via a wired or wireless communicative connection (e.g., to transfer information to one or more other implantable or ambulatory devices, or to an external assembly). In an example, the signal processor 130 can perform one or more signal adjustments such as impedance or level adjustments, among others, before providing the lead motion information to the one or more other portions via the output 140.

FIG. 2 illustrates generally an example of a system 200 that can include an implantable medical device 205. In this example, the implantable medical device 205 can include one or more implantable lead couplings, such as a lead coupling 170. In certain examples, the implantable medical device 205 includes a hermetically-sealed or similar housing 201 coupled to the implantable lead coupling 170. For example, the housing 201 can include titanium or other biocompatible material, such as one or more other conductive materials.

In the example of FIG. 2, the system 200 can include an implantable lead 150 implanted in a heart, such as implanted endocardially via an intravascular route from one or more of a subclavian vein or a femoral artery. In an example, the implantable lead 150 can include one or more conductors, such as one or more concentric or laterally-separated conductors. In an example, one or more conductors can include a braided or coiled shield conductor. The one or more conductors can be insulated from one another and from the environment surrounding the implantable lead 150, such as using a silicone or a poly-ether-ether-ketone (PEEK) insulation, among others. In an example, the conductors to be used for mechanical vibration sensing can be selected based on measurement of RF coupling or an AC impedance between the conductors. Such RF coupling or impedance measurements can be used to determine a conductor pair or combination likely to exhibit higher mechanical vibration sensitivity than other pairs or combinations. Such measurements can also be used to find a conductor pair or combination including an input impedance most closely matched to a conjugate of the output impedance of one or more of a detection circuit, excitation circuit, or interconnect as shown in FIGS. 1, and FIGS. 3-5.

In an example, the implantable medical device 205 can be configured to communicate with the external assembly 210. The communication between the implantable medical device 205 and an external assembly 210 can be wireless or through a wired connection, or using one or more other communication schemes (e.g., using an optical communication link or an acoustic communication link, among others). For example, the external assembly 210 can be a portion or part of a patient management system, such as including or in communication with one or more remote or web-based clients communicatively coupled to one or more servers comprising medical and patient databases.

In an example, the implantable medical device can include one or more of a pacemaker, a defibrillator, an implantable monitor, a drug delivery device, a cardiac resynchronization therapy device, a neural stimulation device, or one or more other implantable assemblies configured to monitor a person or configured to provide one or more treatments to the person. Such monitoring or treatment can include, among others, electrostimulation of tissue such as cardiac tissue, or electrical monitoring of muscular or cardiac activity, among others.

FIG. 3 illustrates generally an example of a system 300 that can include an ambulatory medical device 305, such as including an implantable device as shown in the example of FIG. 2, an externally-worn assembly, or a combination of implantable and external portions. In this example, an excitation circuit 310 can include an oscillator circuit 315 such as configured to provide a first signal. In an example, the oscillator circuit can provide an RF signal (e.g. from about 10 to about 30 megaHertz), such as including a specified current level.

In an example, an interconnect 360 can be coupled to one or more of the excitation circuit 310 or a detection circuit 320. In this example, the first signal (e.g., an excitation current signal) can be provided by the excitation circuit 310 to develop a voltage across two conductors included in the lead coupling 170 via the interconnect 360. For example, the first signal can include one or more current signals provided to one of the conductors, and received from the other conductor. The detection circuit 320 can be configured to receive a second signal (e.g. a developed voltage) across the lead coupling 170.

In an example, the detection circuit 320 can include a demodulation circuit 325. The demodulation circuit 325 can include an envelope detector 323 or a tuned resonant transformer 321 that can be impedance-matched to one or more other attached components. In an example, the envelope detector 323 can demodulate or extract a relatively low frequency component of time-varying voltage from the second signal, such as containing information indicative of motion of an implantable lead 150 attached to the lead coupling 170. The demodulation circuit 325 can be coupled to a signal processor 330. In an example, the signal processor 330 can be configured to extract information indicative of motion of the implantable lead 150, such as including protodiastolic or presystolic gallop sounds, or other mechanical vibrations such as indicative of blood flow, or pressure, among others.

In an example, additional elements can be included in the system 300 to enhance sensitivity or provide additional mechanical event information. For example, multiple implantable leads can be implanted in multiple locations within or on a body and lead motion information can be collected from one or more of the multiple locations. For example, a second lead comprising at least one electrical conductor can be coupled to a second lead coupling, or the implantable lead 150 can include multiple electrical conductors that can be coupled to one or more lead couplings. In an example, one or more mechanical events can provide a change in the impedance of the system comprising the multiple conductors, such as detectable using the second signal provided in response to the first signal. In an example, the signal processor 330 can be coupled to an output 340, and extracted information indicative of motion of the implantable lead 150 can be communicated to another assembly via the output 340. Such other assemblies can include, among others, an additional ambulatory medical device located internally or externally to a body, or an external assembly 210, a combination of one or more implantable and external assemblies.

FIG. 4 illustrates generally an example of a system 400 including ambulatory medical device 405, such as including an implantable device as shown in the example of FIG. 2, an externally-worn assembly, or a combination of implantable and external assemblies. In this example, an excitation circuit 410 can include an oscillator circuit 415 configured to provide a first signal, such as provided to a portion of a detection circuit 420. In an example, an interconnect 460 can be coupled to the detection circuit 420. The detection circuit 420 can include a bridge circuit 421, a capacitive element 425, or an envelope detector 427, among other components or portions. In the example of FIG. 4, the sensitivity of detection circuit 420 can vary with respect to a specified excitation frequency. In an illustrative example, the oscillator circuit 415 can provide a first signal including a sine wave signal with a frequency of around 100 kiloHertz to 1 megaHertz (or including one or more other frequencies). The bridge circuit 421 can include one or more diodes or other rectifiers exhibiting low forward resistance, such as one or more germanium diode (e.g. type 1N60). In this example, the bridge circuit 421 can include resistors of about the same values. The implantable lead 150 can provide a capacitance, and the capacitive element 425 can include a specified capacitance value approximately equal to the capacitance provided by the implantable lead 150 when implantable lead 150 is in equilibrium (e.g., relatively motionless, or subject to a specified baseline of vibration or motion). The capacitance provided by the implantable lead 150 can be one or more capacitances provided between two or more conductors, such as included in a single implantable lead 150, or between conductors respectively included in two or more implantable leads. Generally, the one or more capacitances can be provided by a combination of multiple conductors, and such capacitances can be combined in a series or parallel configuration, such as each including a capacitance contribution from one or more pairs of conductors. In an example, the capacitance can be provided between conductors of physically separate implantable leads. Such lead capacitance can vary in proportion or with respect to motion or vibration coupled to the lead such as from surrounding tissue or blood motion. In an example, the envelope detector 427 can include a relatively high input impedance to achieve a specified sensitivity of the system 400, The envelope detector 427 can include one or more of a diode or rectifier detector, or a synchronous detector, such as to improve noise rejection, selectivity, or one or more other characteristics.

In an example, a signal processor 430 can be configured to receive a signal from the detection circuit 420, such as provided at least in part by the envelope detector 427. For example, the signal processor 430 can be configured to extract information from the received voltage signal indicating a motion of an implantable lead 150. In an example, the signal processor 430 can include a low pass filter circuit to process the signal received from the detection circuit 420. In an example, the signal processor 430 includes an amplification circuit, or one or more other circuits or components, such as to amplify the received signal. In an example, the signal processor 430 can include an analog-to-digital converter to convert the information indicative of motion into a digital data signal, such as for storage, further processing, or for presentation to a caregiver or clinician.

In an example, an output 440 can be configured to receive a signal from the signal processor 430, and the output 440 can be configured to transfer the information indicative of motion of the implantable lead 150 to another implantable or ambulatory medical device, or to an external assembly such as the external assembly 210 using a wireless or wired communicative coupling, In an example, the output 440 can be configured to communicate with one or more external assemblies including one or more tabletop or handheld electronic devices (e.g. a cell phone, smart phone, tablet, laptop, or personal digital assistant (PDA), among others), in addition to or instead of one or more external assemblies dedicated for medical diagnosis or assessment.

In an illustrative example, one or more of the detection circuit 420 or the signal processor 430 can receive a second signal in response to the first signal, and the second signal can include a portion in-phase with the first signal, and a second portion in quadrature (e.g., ninety degrees out of phase) with the first signal. In this illustrative example, the detection circuit 420 or the signal processor 430 can use the quadrature component of the second signal to determine the change in capacitance of the lead system, thus canceling out the effect of the resistive component of an impedance presented by the lead 150 to the measurement circuit.

FIG. 5 illustrates generally an example of a system 500 including ambulatory medical device 505, such as including an implantable device as shown in the example of FIG. 2, or an externally-worn assembly. In this example, au excitation circuit 510 can include a pulse generator circuit 515 configured to provide a first signal, and a detection circuit 520. In an example, the detection circuit 520 can include a multiplexer 521, a capacitive element 525, or a voltage detector 527. In an example, the multiplexer 521 can be configured to select among one or more inputs, wherein the inputs can be coupled to the excitation circuit 510, or another signal-generating source. In an example, the multiplexer 521 can be under the control of the detection circuit 520 or another component of the ambulatory medical device 505. An interconnect 560, the voltage detector 527, or a lead coupling 170, among other components, can be coupled to the multiplexer 521.

One or more portions of the system 500 , such as the interconnect 560, multiplexer 521, or voltage detector 527, can be implemented on a rigid or flexible circuit board, such as including one or more application specific integrated circuits, among other components. In an example, the lead coupling 170 can be implemented via an electrical and mechanical interconnect in a header block that can be attached to the housing 201 of an implantable medical device housing, such as shown in FIG. 2. The housing 201 of the implantable medical device itself can be used as one of the conductors for capacitance or impedance measurement,

In an example, the excitation circuit 510 can be coupled to the multiplexer 521. In an example, the multiplexer 521 can be configured to couple the excitation circuit 510 to each of the interconnect 560 and the capacitive element 525, concurrently or successively. In an example, the concurrent or successive coupling can be performed by the multiplexer 521 under the direction of a logic circuit included as a portion of the detection circuit 520, For example, the logic circuit can include a counter or timer such as to provide one or more counts or durations to be used by the logic circuit to switch the state of the multiplexer 521, such as after a specified duration of time elapses as indicated by the counter or timer. In an example, the logic circuit can be configured to count a number of pulses provided by the excitation circuit 510. In this example, the logic circuit can be configured to switch the state of the multiplexer 521, such as after a specified count of a number of pulses is met or exceeded as indicated by the counter.

In the example of FIG. 5, the multiplexer 521 can be configured to couple the first signal to a first capacitance provided by implantable lead 150. In an example, a first voltage can be developed across the first capacitance in response to the first signal. A second signal that includes the first voltage can be received by the voltage detector 527. In this example, a signal processor 530 can receive the output of the voltage detector 527. In an example, the signal processor 530 can be configured to compare the received signal from the first capacitance to a threshold voltage (e.g., monitoring a charging of the first capacitance to reach the specified threshold voltage).

In the example of FIG. 5, the multiplexer 521 can be configured to couple the first signal to a second capacitance provided by the capacitive element 525 (e.g., a “reference capacitance,” charged using the same or a similar first signal). In an example, the multiplexer 521 can be configured to provide the first signal to each of the first capacitance and second capacitance, either separately, sequentially, or in combination. In an example, a second voltage can be developed across the second capacitance in response to the first signal. In an example, the second signal that includes the second voltage can be received by the voltage detector 527. In this example, a signal processor 530 can receive the output of the voltage detector 527. In an example, the signal processor 530 can be configured to compare the received signal from the second capacitance to the specified threshold voltage (e.g., monitoring a charging of the second “reference” capacitance to reach the specified threshold voltage).

In the example of FIG. 5, the signal processor 530 can be configured to determine a relative indication of information (e.g., a ratio, a difference, etc.) derived from one or more of the first or second voltages measured with respect to the first or second capacitances. Coupling of mechanical vibration to the implantable lead 150, or other motion of the lead, can cause a detectable change in the capacitance of the lead. For example, the second signal received from the first capacitance can differ from the second signal received from the second capacitance in response to a similar excitation by the first signal. In this manner, a variation between a reference capacitance (e.g., provided by capacitive element 525) and the capacitance of the lead can be used to provide information corresponding to motion of the implantable lead. In an example, capacitive element 525 can include, among other things, an additional specified capacitance such as provided by a discrete capacitor, a second implantable lead or combination of conductors, a number of interconnected implantable leads, or a capacitive transducer.

In the example of FIG. 5, the first signal can charge the first capacitance to a first specified threshold voltage, and a corresponding duration of the charge time can be determined (e.g., such as when the first capacitance is charged using a sequence of current pulses or a constant current). In au example, the voltage detector 527 can be configured to receive the first voltage in response to the charging of the first capacitance. In this example, the signal processor 530 can be configured to determine a duration of a first charge time, corresponding to a duration where the first voltage is between a lower threshold (e.g., around 0 Volts), and an upper threshold (e.g., the first specified voltage threshold). In an example, the signal processor 530 can be configured to determine a duration of a second charge time, corresponding to a duration where the second voltage is between the lower and upper thresholds. If the capacitance of the capacitive element 525 and the lead capacitance are roughly equal, the determined first and second charge times can be roughly equal, such as when the lead 150 is at rest or equilibrium.

In the example of FIG. 5, the excitation signal (e.g., the first signal), can include a series of current pulses having a specified peak current level, duration, pulse repetition rate, duty cycle, etc. The signal processor 530 can be configured to count a number of pulses delivered to the lead 150, or to a capacitive element 525. For example, the voltage detector 527 can be configured to receive pulsed signals and the signal processor 530 can be configured to count the received pulsed signals. In an example, the signal processor 530 can be configured to count a first count of a number of pulses provided to the first capacitance, such as to reach the specified threshold voltage (e.g., the pulse count can be a proxy for a measurement of a charge time duration, such as when pulses of determinable width and level are used). In an example, the signal processor 530 can be configured to extract from the first count an indication of lead motion, since the variation in the lead capacitance can provide a difference in a number of pulses needed to reach the specified threshold, such as compared with a baseline number of pulses corresponding to a lead at rest or in equilibrium.

In an example, the sensitivity of the system 500 can be enhanced by using a comparison between a second capacitance (e.g., a reference capacitance or another pair or combination of lead conductors) and the capacitance of the lead 150. The signal processor 530 can be configured to count a second count of a number of pulses provided to the second capacitance (e.g., using a series of pulses of determinable width or level, as above). For example, the signal processor 530 can be configured to extract from the first and second counts a relative indication of information that can indicate lead motion (e.g., a difference, or ratio, etc., between the first and second counts of pulses). In an illustrative example, the signal processor 530 can measure multiple pulse durations and perform comparison operations, such as including using one or more techniques disclosed in Pelletier et al. U.S. Pat. No. 4,011,500 entitled “PHYSICAL DISPLACEMENT SENSING WITH DIFFERENTIAL CAPACITOR,” which is hereby incorporated by reference in its entirety, including its disclosure of using a differential capacitor to detect a physical displacement.

In an example, an output 540 can be configured to receive information from the signal processor 530, and to transfer such information to one or more other portions of the ambulatory medical device 505, or to communicate with an external assembly.

FIG. 6 illustrates generally an example 600 that can include providing a first signal, receiving a second signal, or extracting information indicative of lead motion from the second signal, such as using circuitry or techniques as discussed above in the examples of FIGS. 1-5.

At 610, a first signal can be provided to excite the ambulatory medical device 105. In an example, the first signal can be a non-tissue-stimulating electrical signal. For example, the first signal can be an AC signal generated or provided by an excitation circuit 110. In an example, the first signal can be provided to an implantable lead 150.

At 630, a second signal can be received in response to the first signal. In an example, the detection circuit 120 can be configured to receive the second signal from the implantable lead 150. In an example, the second signal can include, among other signals, a phase-shifted or modulated version of the first signal, a voltage signal, a logic signal, or a data signal including information indicative of motion of the implantable lead.

At 650, information can be extracted from the second signal. The extracted information can indicate motion of the implantable lead 150. In an example, the information can indicate a relative or absolute indication of a displacement of the implantable lead 150. In an example, the information can include an electrical representation of mechanical vibration or motion coupled to the lead, such as including a heart sound, a blood pressure sound, or respiratory sound, among others.

FIG. 7 illustrates generally an example 700 that can include generating an oscillating first signal, providing the first signal to an implantable lead, receiving a second signal from the implantable lead, demodulating the second signal, or extracting information indicative of lead motion, such as using circuitry or techniques discussed above with respect to FIGS. 1-5.

At 705, a first signal can be generated by an oscillator circuit included in an excitation circuit 110. In an example, the oscillator circuit can include a Colpitts oscillator, In an example, the first signal can include an AC signal and the frequency of oscillation can be tunable such as to achieve a specified sensitivity.

At 710, the first signal can be provided to the implantable lead 150, such as via an interconnect 360 and a lead coupling 170. In an example, the first signal can be coupled through a series capacitor with high DC or near-DC impedance to create a relatively constant current signal into the implantable lead 150. In an example, a change in capacitance of the implantable lead 150 can modulate the impedance of the circuit comprising the implantable lead 150, the lead coupling 170, and the interconnect 360.

At 730, a second signal can be received from the implantable lead 150, such as in response to the first signal. In an example, the modulated impedance of the circuit comprising the implantable lead 150, the lead coupling 170, and the interconnect 360 can produce the second signal in response to the first signal such that the second signal can be different than the first signal.

At 740, the second signal can be demodulated to recover the information indicative of lead motion, In an example, the second signal can be received by a detection circuit 320 wherein a demodulation circuit 325 can be used to demodulate the received second signal. The demodulation circuit 325 can include a tuned resonant transformer 321 or an envelope detector 323, wherein the transformer 321 can be configured to provide an impedance-matched coupling between the second signal and the envelope detector. In an example, the second signal can include a voltage that can be detected between conductors in the implantable lead 150, including a voltage that can include a phase-shifted version of the first signal. In this example, information indicative of lead motion can be realized by extracting a relatively low frequency component of a time-varying voltage from the second signal using the envelope detector 323. In an example, the second signal comprises a large DC voltage with a small AC voltage superimposed, wherein the AC voltage can result from the response of the first signal to the modulated impedance. In an example, the implantable lead 150 can be implanted in a heart and provided with the first signal. In this example, the resulting AC component of the second signal can include information about heart wall motion (or information indicative of one or more other mechanical vibrations coupled to the lead 150).

At 750, information can be extracted from the demodulated second signal that can indicate motion of the implantable lead 150. In an example, the second signal can be received from the implantable lead 150. In an example, the second signal can be relatively constant over time (e.g., relatively constant in frequency or in amplitude, among other parameters) for a stationary or immobilized implantable lead 150 because the impedance of the implantable lead 150 can remain relatively unchanged at equilibrium. However, as the implantable lead 150 undergoes movement (or as mechanical vibration is coupled to the lead), the movement of the implantable lead 150 can modulate or change the impedance of the system containing the one or more conductors in the implantable lead 150, and the second signal can deviate from its relatively constant amplitude or frequency. For example, a mechanical vibration coupled to the implantable lead 150 can produce a microphonic effect such as receiving the vibration information by the implantable lead 150 and providing a second signal in response to the first signal that is analogous to the received vibration. In this example, the mechanical vibration is effectively translated to an analogous electrical signal.

In an example, more than one implantable lead can be included in the ambulatory medical device 300, as previously described. In this example, the first signal can be provided to the system comprising the multiple implantable leads and the second signal can be received from the same system. In an example, the relative or independent motion of the two or more leads can modulate the impedance of the system comprising the leads. In an example, the additional leads can provide a greater magnitude of impedance modulation of the system comprising the sensing elements, therefore exaggerating the response signal under some circumstances (e.g., using a “differential” measurement of multiple lead impedances or capacitances). Under some other set of circumstances, the impedance modulation of the system comprising the multiple sensing elements may have a nullifying effect on the response signal. In such an example, the implantable leads can be implanted or configured, or the conductors used for sensing can be selected, in such a manner as to create a specified response or sensitivity.

In an example, the demodulated signal can be provided to a signal processor 330 for further extracting the information indicative of motion of the implantable lead 150. In an example, the second signal can be high pass filtered to remove the low frequency wall motion and isolate higher frequency blood flow motion information. In this example, the pitch of the resulting signal can be related to the velocity of the blood flow. In an example, a demodulated and filtered signal can be transmitted, such as via an output 340, to an external assembly, such as for visual or audible presentation to a clinician or care giver, such as using an audio amplifier. In an example, an examiner can listen to the blood flow information or the heart wall motion information provided by the medical device. For example, when the information indicative of motion includes a subsonic or ultrasonic component, such components can be respectively upconverted or downconverted (e.g., adjusted in speed or frequency) for playback using an audible range of frequencies.

FIG. 8 illustrates generally an example 800 that can include generating an oscillating first signal, providing the first signal to an implantable lead, receiving a second signal from the implantable lead, receiving a voltage signal, or extracting information indicative of lead motion from the voltage signal, such as using circuitry or techniques discussed above with respect to FIGS. 1-5.

At 805, a first signal can be generated by an oscillator circuit included in excitation circuit 110. In an example, the oscillator circuit can include a Pierce oscillator. In an example, the frequency of oscillation can in part determine the sensitivity of a system 400. The frequency of the first signal can be specified to correspond to one or more frequencies that exhibit a change in impedance of an implantable lead 150 at least in part due to motion of the implantable lead 150.

At 810, a first signal can be provided to the implantable lead 150. In an example, the first signal can be an AC signal routed through a bridge circuit 421. In this example, the implantable lead 150 can form a portion (e.g., one of the legs) of the bridge circuit 421. In an example, a capacitive element 425 forms the leg of the bridge circuit 421 that is opposite the implantable lead 150. In an example, positive half cycles of the first signal can charge a first capacitance provided by the implantable lead 150. In an example, the capacitive element 425 can act as a second capacitance, which can be charged during negative half cycles of the first signal.

At 830, a second signal can be received from the implantable lead 150 wherein the second signal can be a response to the first signal. In an example, the second signal can be a voltage signal indicating a voltage across the first capacitance, and thus a change in capacitance of the implantable lead 150 can be transformed into a voltage signal. The second signal can be a voltage signal indicating a voltage across the second capacitance.

At 840, the voltage signal can be received. In an example, a voltage signal indicating a change in capacitance can be received by the envelope detector 427. In an example, the envelope detector 427 can be a diode or rectifier detector or a synchronous detector operating at the same frequency as the first signal. In an example, the voltage across the envelope detector 427 can include a relatively constant value (e.g., amplitude or frequency) when the implantable lead 150 is at equilibrium. However, when the capacitance of implantable lead 150 changes, such as during a movement of the implantable lead 150, the voltage across the envelope detector 427 can change by an amount proportional to the displacement of the implantable lead 150, the magnitude of the change in capacitance indicative of displacement.

At 850, information can be extracted from the envelope detector 427 that can be indicative of motion of the implantable lead 150. In an example, a signal can be transmitted to an external source and amplified by an audio amplifier. In an example, an examiner can listen to heart sound information, as discussed above in the example of FIG. 7. In an example, heart wall motion information can be isolated and visually or audibly presented to the examiner (e.g., a clinician or caregiver).

FIG. 9 illustrates generally an example 900 that can include generating a pulsed first signal, providing the first signal to an implantable lead, receiving a voltage, or extracting information indicative of lead motion, such as using circuitry or techniques discussed above with respect to FIGS. 1-5.

At 905, a first signal can be generated by a pulse generator. In an example, the pulse generator can produce a sequence of square wave pulses, or pulses having one or more other specified levels, duty cycles, repetition rates, or the like.

At 910, a first signal can be provided to an implantable lead 150. In an example, a first signal can be received from the excitation circuit 510 by the detection circuit 520. The received first signal can be coupled to the multiplexer 521 in detection circuit 520. In an example, the multiplexer 521 can be coupled to the implantable lead 150 via the interconnect 560 and the lead coupling 170. In an example, the detection circuit 520 can include a multiplexer 521 that can control the coupling of the first signal to the implantable lead 150. The multiplexer 521 can also be configured to apply a first signal to the capacitive element 525.

At 940, a voltage signal can be received. In an example, the multiplexer 521 can be configured to apply a first signal to the implantable lead 150 for a specified duration of time. In an example, the voltage signal can include a first voltage measurement of the implantable lead after a specified duration of time. In an example, the multiplexer 521 can be configured to apply a first signal to the capacitive element 525 for a specified duration of time (e.g., to charge the capacitive element 525). The voltage signal can include a second voltage measurement of the capacitive element 525 after a specified duration of time.

At 950, information can be extracted from one or more of the first or second voltage signals indicative of motion of an implantable lead 150. In an example, the voltage signal can be compared to a specified threshold voltage, or one or more voltage signals can be compared to an array of threshold voltages.

FIG. 10 illustrates generally an example 1000 that can include generating a pulsed first signal, providing the pulsed first signal to a first capacitance, providing the pulsed first signal to a second capacitance, receiving a first voltage, receiving a second voltage, or extracting information indicative of lead motion.

At 1005, a first signal can be generated by a pulse generator. In an example, the pulse generator can produce pulses such as including one or more current or voltage pulses including pulses of a specified amplitude, duty cycle, or morphology, among other parameters.

At 1010, a first signal can be provided to a first capacitance. In an example, the first capacitance can be provided at least in part by the implantable lead 150. In an example, the first signal can be received from the excitation circuit 510 by the detection circuit 520. The received first signal can be coupled to the multiplexer 521 in the detection circuit 520. The multiplexer 521 can be coupled to the implantable lead 150 via the interconnect 560 and the lead coupling 170. In an example, the detection circuit 520 can operate the multiplexer 521 to determine when a first signal can be applied to the implantable lead 150.

At 1020, the first signal can be similarly provided to the second capacitance. For example, the second capacitance can be provided by the capacitive element 525. In an example, the multiplexer 521 can be coupled to the capacitive element 525. In an example, the detection circuit 520 can operate the multiplexer 521 to controllably couple the first signal to the second capacitance. The capacitive element 525 can be a discrete or distributed capacitor or a combination of capacitors providing a specified capacitance value, a second implantable lead, or an array of interconnected implantable leads or conductors, among others.

At 1030, a first voltage signal can be received. The first voltage signal can be a signal in response to the first signal. In an example, the first voltage signal can indicate, among other things, a charge level of the first capacitance or a first count of a number of pulses provided by the first signal.

At 1040, the second voltage signal can be received. The second voltage signal can be a signal in response to the first signal. In an example, the second voltage signal can indicate, among other things, a charge level of the second capacitance or a second count of a number of pulses provided by the first signal.

At 1050, information can be extracted from the first and second voltage signals indicative of motion of the implantable lead 150. In an example, the first and second voltage signals can represent, respectively, a duration of respective first and second capacitor charge times. In this example, the first charge time can include an interval wherein the voltage across the first capacitance is between a lower voltage threshold and an upper voltage threshold. Similarly, the second charge time can include an interval wherein the voltage across the second capacitance is between the lower and upper voltage thresholds. In an example, information indicative of lead motion can be extracted by determining a relative indication of the first and second durations. For example, the first duration can be measured to be greater or lesser than the second duration. For example, the difference between the first and second durations can indicate the magnitude of the displacement of the implantable lead 150, wherein the displacement causes a change in the first capacitance. In an example, when the first and second duration of a charge time are approximately equivalent, the relative indication of information can indicate that the implantable lead 150 is stationary or otherwise at equilibrium.

In an example, the first voltage signal can represent a first count of a number a pulses provided to the first capacitance. Similarly, the second voltage signal can represent a second count of a number of pulses provided to the second capacitance.

In an example, information indicative of lead motion can be extracted by determining a relative indication of the first and second counts. For example, the difference between the first and second counts can indicate the magnitude of the displacement of the implantable lead 150, wherein the displacement causes a change in the first capacitance. In an example, when the first and second counts are approximately equivalent or unchanging, the relative indication of information can indicate that the implantable lead 150 is stationary or otherwise at equilibrium.

Additional Notes & Examples

Example 1 describes subject matter that can include a system. The system can comprise an excitation circuit configured to be electrically coupled to a first implantable lead. The excitation circuit can be further configured to provide a non-tissue-stimulating first signal to the first implantable lead. A detection circuit can be included. The detection circuit can be configured to be electrically coupled to the first implantable lead and configured to receive a second signal in response to the first signal, from the first implantable lead. The second signal can be determined at least in part by a motion of the implantable lead. A signal processor circuit can be included. The signal processor circuit can be coupled to the detection circuit and can be configured to extract information indicative of motion of the first implantable lead, such as via demodulation of the second signal.

In Example 2, the subject matter of Example 1 can optionally include the first signal including an oscillating signal, wherein an implantable lead can be configured to modulate the oscillating signal at least in part via the motion of the implantable lead to provide a second signal, and wherein the detection circuit can be configured to demodulate the second signal.

In Example 3, the subject matter of one or any combination of Examples 1-2 can optionally include the information indicative of motion of the implantable lead, including lead impedance information indicative of a mechanical physiological event.

In Example 4, the subject matter of one or any combination of Examples 1-3 can optionally include the information indicative of motion of the implantable lead including information indicative of a mechanical vibration of a heart, the mechanical vibration coupled to the lead when the implantable lead is optionally located in or near the heart.

In Example 5, the subject matter of one or any combination of Examples 1-4 can optionally include the information indicative of motion including information indicative of a blood pressure when the lead is optionally located in or near a blood vessel.

In Example 6, the subject matter of one or any combination of Examples 1-5 can optionally include an implantable lead.

In Example 7, the subject matter of one or any combination of Examples 1-6 can optionally include an implantable lead comprising a conductor configured to carry therapy energy, and wherein at least one of the first signal or the second signal can be coupled to the conductor configured to carry therapy energy.

In Example 8, the subject matter of one or any combination of Examples 1-7 can optionally include an implantable lead configured to provide a capacitance. The excitation circuit can optionally be configured to charge the capacitance, and the detection circuit can be configured to detect a voltage indicative of a change in the capacitance, the voltage determined at least in part by the motion of the implantable lead.

In Example 9, the subject matter of one or any combination of Examples 1-8 can optionally include an implantable lead configured to provide a first capacitance, wherein the excitation circuit can be configured to charge the first capacitance using the first signal including a pulsed signal, wherein the second signal includes a first voltage developed across the first capacitance, and wherein the signal processor circuit can be configured to compare the first voltage to a specified first threshold.

In Example 10, the subject matter of one or any combination of Examples 1-9 can optionally include a second capacitor, wherein the excitation circuit can be configured to charge the second capacitance using the first signal including the pulsed signal, wherein the detection circuit can be configured to receive a second voltage developed across the second capacitance, and wherein the signal processor circuit can be configured to determine a relative indication of information derived from one or more of the first or second voltages, the relative indication of information corresponding at least in part to the motion of the implantable lead.

In Example 11, the subject matter of one or any combination of Examples 1-10 can optionally include a signal processor circuit configured to (1) determine a duration of a first charge time, wherein the first charge time includes an interval wherein the first capacitance can be between a lower voltage threshold and an upper voltage threshold, or (2) count a first count of a number of pulses, provided to the first capacitance. The signal processor circuit can optionally be configured to (1) determine a duration of a second charge time, wherein the second charge time includes an interval wherein the second capacitance can be between the lower voltage threshold and the upper voltage threshold, or (2) count a second count of a number pulses, provided to the second capacitance. The signal processor circuit can optionally be configured to determine the relative indication of information using (1) the duration of the first and second charge times, or (2) the first and second counts.

In Example 12, the subject matter of one or any combination of Examples 1-11 can optionally include the relative indication of information including a difference between the first and second counts.

In Example 13, the subject matter of one or any combination of Examples 1-12 can optionally include the relative indication of information including a difference between the first and second pulse durations.

In Example 14, the subject matter of one or any combination of Examples 1-13 can optionally include the relative indication of information including a ratio of the first and second counts,

In Example 15, the subject matter of one or any combination of Examples 1-14 can optionally include the relative indication of information including a ratio of the first and second pulse durations.

In Example 16, the subject matter of one or any combination of Examples 1-15 can optionally include an ambulatory medical device, comprising an excitation circuit configured to be electrically coupled to an implantable lead, the excitation circuit configured to provide a non-tissue-stimulating first signal to the implantable lead when the implantable lead is optionally implanted at a tissue site. A detection circuit can be included and can be configured to be electrically coupled to the implantable lead and configured to receive a second signal, in response to the first signal, from the implantable lead, wherein the second signal can be determined at least in part by a motion of the implantable lead. A signal processor circuit can be included, and can be configured to be coupled to the detection circuit, the signal processor circuit configured to extract information indicative of motion of the implantable lead, wherein the first signal can include an oscillating signal, and wherein the implantable lead can be configured to modulate the oscillating signal at least in part using the motion of the implantable lead to provide the second signal, and wherein the detection circuit can be configured to demodulate the second signal. The detection circuit can optionally include a bridge rectifier circuit, such as a diode bridge rectifier circuit, configured to demodulate or detect an envelope of the second signal.

Example 17 can include, or can optionally be combined with one or any combination of Examples 1-16 to include, subject matter that can include: using an ambulatory medical device, providing a first signal to an implantable lead, the first signal generated by an excitation circuit and provided at a non-tissue-stimulating energy level, and receiving, from the implantable lead, a second signal in response to the first signal, wherein the second signal can be determined at least in part by a motion of the implantable lead within a body, and extracting, from the signal obtained in response to the excitation signal, information indicative of the motion of the implantable lead.

In Example 18, the subject matter of one or any combination of Examples 1-17 can optionally comprise the first signal including an oscillating signal, and wherein receiving the second signal can include receiving a second signal modulated at least in part by the motion of the implantable lead, and wherein the extracting information indicative of the motion can include demodulating the second signal.

In Example 19, the subject matter of one or any combination of Examples 1-18 can optionally comprise the information indicative of the motion of the implantable lead including information indicative of a mechanical vibration of a heart, the mechanical vibration coupled to the implantable lead when the implantable lead is optionally located in or near the heart.

In Example 20, the subject matter of one or any combination of Examples 1-19 can optionally comprise the information indicative of the motion of the implantable lead including information indicative of a blood pressure when the implantable lead is optionally located in or near a blood vessel.

In Example 21, the subject matter of one or any combination of Examples 1-20 can optionally comprise receiving the second signal from the implantable lead including receiving a voltage indicative of a change in a capacitance provided by the implantable lead, and wherein the extracting information indicative of the motion includes measuring the received voltage.

In Example 22, the subject matter of one or any combination of Examples 1-21 can optionally comprise the first signal, including a pulsed signal provided to a first capacitance provided by the lead, and can optionally further comprise charging the first capacitance using the pulsed signal, wherein the receiving the information can include receiving a first voltage developed across the first capacitance, and wherein the extracting information indicative of the motion can include comparing the first voltage to a specified first threshold.

In Example 23, the subject matter of one or any combination of Examples 1-22 can optionally comprise charging a second capacitance using the pulsed signal, receiving a second voltage signal developed across the second capacitance, and wherein the extracting information indicative of the motion can include determining a relative indication of information derived from one or more of the first or second voltages, the relative indication of information corresponding at least in part to the motion of the implantable lead,

In Example 24, the subject matter of one or any combination of Examples 1-23 can optionally comprise a detection circuit including an envelope detector. The envelope detector can be configured to demodulate a received signal, such as a signal received from one or more implantable leads. The detection circuit can be configured to extract an indication of a time-varying signal, such as a time-varying voltage.

In Example 25, the subject matter of one or any combination of Examples 1-24 can optionally comprise a resonant transformer. The resonant transformer can be impedance-matched to an implantable lead.

In Example 26, the subject matter of one or any combination of Examples 1-25 can optionally comprise a first implantable lead and a second implantable lead. The first implantable lead can include a first conductor configured to carry therapy energy, and the second implantable lead can include a second conductor configured to carry therapy energy. An excitation circuit can be configured to be electrically coupled to the second implantable lead, and can be configured to provide a non-tissue-stimulating first signal to the first and second implantable leads. A detection circuit can be configured to be electrically coupled to the first and second implantable leads, and can be configured to detect a capacitance using the first conductor of the first implantable lead and the second conductor of the second implantable lead.

In Example 27, the subject matter of one or any combination of Examples 1-26 can optionally comprise a detection circuit, including a synchronous detector. The synchronous detector can be configured to perform synchronous demodulation, such as using a local oscillator signal on a frequency approximately the same as a carrier frequency. The carrier frequency can be a characteristic parameter of a first signal, such as can be provided to an implantable lead. The synchronous detector can improve a signal-to-noise ratio, such as compared to a diode-based envelope detector.

In Example 28, the subject matter of one or any combination of Examples 1-27 can optionally comprise a detection circuit configured to use a quadrature component of a received signal, such as in response to a first signal provided to an implantable lead, to indicate a change in capacitance of the implantable lead.

These examples can be combined with each other or with the other subject matter described herein in any permutation or combination.

The above detailed description includes references to the accompanying drawings, which form a part of the detailed description. The drawings show, by way of illustration, specific embodiments in which the invention can be practiced.

These embodiments are also referred to herein as “examples.” Such examples can include elements in addition to those shown or described. However, the present inventors also contemplate examples in which only those elements shown or described are provided. Moreover, the present inventors also contemplate examples using any combination or permutation of those elements shown or described (or one or more aspects thereon, either with respect to a particular example (or one or more aspects thereof), or with respect to other examples (or one or more aspects thereof) shown or described herein.

All publications, patents, and patent documents referred to in this document are incorporated by reference herein in their entirety, as though individually incorporated by reference. In the event of inconsistent usages between this document and those documents so incorporated by reference, the usage in the incorporated reference(s) should be considered supplementary to that of this document; for irreconcilable inconsistencies, the usage in this document controls.

In this document, the terms “a” or “an” are used, as is common in patent documents, to include one or more than one, independent of any other instances or usages of “at least one” or “one or more.” In this document, the term “or” is used to refer to a nonexclusive or, such that “A or B” includes “A but not B,” “B but not A,” and “A and B,” unless otherwise indicated. In this document, the terms “including” and “in which” are used as the plain-English equivalents of the respective terms “comprising” and “wherein,” Also, in the following claims, the terms “including” and “comprising” are open-ended, that is, a system, device, article, or process that includes elements in addition to those listed after such a term in a claim are still deemed to fall within the scope of that claim. Moreover, in the following claims, the terms “first,” “second,” and “third,” etc. are used merely as labels, and are not intended to impose numerical requirements on their objects.

Method examples described herein can be machine or computer-implemented at least in part. Some examples can include a computer-readable medium or machine-readable medium encoded with instructions operable to configure an electronic device to perform methods as described in the above examples. An implementation of such methods can include code, such as microcode, assembly language code, a higher-level language code, or the like. Such code can include computer readable instructions for performing various methods. The code may form portions of computer program products. Further, in an example, the code can be tangibly stored on one or more volatile, non-transitory, or non-volatile tangible computer-readable media, such as during execution or at other times. Examples of these tangible computer-readable media can include, but are not limited to, hard disks, removable magnetic disks, removable optical disks (e.g., compact disks and digital video disks), magnetic cassettes, memory cards or sticks, random access memories (RAMS), read only memories (ROMs), and the like. The above description is intended to be illustrative, and not restrictive. For example, the above-described examples (or one or more aspects thereof) may be used in combination with each other. Other embodiments can be used, such as by one of ordinary skill in the art upon reviewing the above description. The Abstract is provided to comply with 37 C.F.R. §1.72(b), to allow the reader to quickly ascertain the nature of the technical disclosure. It is submitted with the understanding that it will not be used to interpret or limit the scope or meaning of the claims. Also, in the above Detailed Description, various features may be grouped together to streamline the disclosure. This should not be interpreted as intending that an unclaimed disclosed feature is essential to any claim. Rather, inventive subject matter may lie in less than all features of a particular disclosed embodiment. Thus, the following claims are hereby incorporated into the Detailed Description, with each claim standing on its own as a separate embodiment, and it is contemplated that such embodiments can be combined with each other in various combinations or permutations. The scope of the invention should be determined with reference to the appended claims, along with the full scope of equivalents to which such claims are entitled. 

1. A system, comprising: an ambulatory medical device, comprising: an excitation circuit configured to be electrically coupled to a first implantable lead, the excitation circuit configured to provide a non-tissue-stimulating first signal to the first implantable lead; a detection circuit configured to be electrically coupled to the first implantable lead and configured to receive a second signal, in response to the first signal, from the first implantable lead, wherein the second signal is determined at least in part by a motion of the first implantable lead; and a signal processor circuit, coupled to the detection circuit, the signal processor circuit configured to extract information indicative of motion of the first implantable lead via demodulation of the second signal.
 2. The system of claim 1, wherein the detection circuit includes an envelope detector configured to demodulate the received second signal and extract an indication of a time-varying voltage.
 3. The system of claim 1, wherein the first signal includes an oscillating signal; wherein the implantable lead is configured to modulate the oscillating signal at least in part via the motion of the implantable lead to provide the second signal; and wherein the detection circuit is configured to demodulate the second signal.
 4. The system of claim 1, wherein the information indicative of motion of the implantable lead includes lead impedance information indicative of a mechanical physiological event.
 5. The system of claim 1, wherein the information indicative of motion of the implantable lead includes information indicative of a mechanical vibration of a heart, the mechanical vibration coupled to the lead when the implantable lead is located in or near the heart.
 6. The system of claim 1, further comprising the first implantable lead.
 7. The system of claim 6, wherein the detection circuit includes a resonant transformer that is impedance-matched to the first implantable lead.
 8. The system of claim 6, wherein the first implantable lead comprises a first conductor configured to carry therapy energy; and wherein at least one of the first signal or the second signal is coupled to the first conductor configured to carry therapy energy.
 9. The system of claim 6, wherein the implantable lead is configured to provide a first capacitance; and wherein the excitation circuit is configured to charge the first capacitance; and wherein the detection circuit is configured to detect a voltage indicative of a change in the first capacitance, the voltage determined at least in part by the motion of the implantable lead.
 10. The system of claim 9, further comprising a second implantable lead including a second conductor configured to carry therapy energy; wherein the excitation circuit is configured to be electrically coupled to the second implantable lead, and is configured to provide the non-tissue-stimulating first signal to the first and second implantable leads; and wherein the detection circuit is configured to be electrically coupled to the first and second implantable leads, and is configured to detect a capacitance using the first conductor of the first implantable lead and the second conductor of the second implantable lead.
 11. The system of claim 6, wherein the implantable lead is configured to provide a first capacitance; wherein the excitation circuit is configured to charge the first capacitance using the first signal including a pulsed signal; wherein the second signal includes a first voltage developed across the first capacitance; and wherein the signal processor circuit is configured to compare the first voltage to a specified first threshold.
 12. The system of claim 11, comprising a second capacitor; wherein the excitation circuit is configured to charge the second capacitance using the first signal including the pulsed signal; wherein the detection circuit is configured to receive a second voltage developed across the second capacitance; and wherein the signal processor circuit is configured to determine a relative indication of information derived from one or more of the first or second voltages, the relative indication of information corresponding at least in part to the motion of the implantable lead.
 13. The system of claim 12, wherein the signal processor circuit is configured to (1) determine a duration of a first charge time, wherein the first charge time includes an interval wherein the first capacitance is between a lower voltage threshold and an upper voltage threshold, or (2) count a first count of a number of pulses, provided to the first capacitance; and wherein the signal processor circuit is configured to (1) determine a duration of a second charge time, wherein the second charge time includes an interval wherein the second capacitance is between the lower voltage threshold and the upper voltage threshold, or (2) count a second count of a number pulses, provided to the second capacitance; and wherein the signal processor circuit is configured to determine the relative indication of information using (1) the duration of the first and second charge times, or (2) the first and second counts.
 14. A system, comprising: an ambulatory medical device, comprising: an excitation circuit configured to be electrically coupled to an implantable lead, the excitation circuit configured to provide a non-tissue-stimulating first signal to the implantable lead when the implantable lead is implanted at a tissue site; a detection circuit configured to be electrically coupled to the implantable lead and configured to receive a second signal, in response to the first signal, from the implantable lead, wherein the second signal is determined at least in part by a motion of the implantable lead; a signal processor circuit, coupled to the detection circuit, the signal processor circuit configured to extract information indicative of motion of the implantable lead; wherein the first signal includes an oscillating signal; wherein the implantable lead is configured to modulate the oscillating signal at least in part via the motion of the implantable lead to provide the second signal; and wherein the detection circuit includes a bridge rectifier circuit configured to demodulate the second signal.
 15. A method comprising: using an ambulatory medical device, providing a first signal to an implantable lead, the first signal generated by an excitation circuit and provided at a non-tissue-stimulating energy level; receiving, from the implantable lead, a second signal in response to the first signal, wherein the second signal is determined at least in part by a motion of the implantable lead within a body; and extracting, from the signal obtained in response to the excitation signal, information indicative of the motion of the implantable lead,
 16. The method of claim 15, wherein the first signal includes an oscillating signal; and wherein receiving the second signal includes receiving a second signal modulated at least in part by the motion of the implantable lead; and wherein the extracting information indicative of the motion includes demodulating the second signal.
 17. The method of claim 15, wherein the information indicative of the motion of the implantable lead includes information indicative of a mechanical vibration of a heart, the mechanical vibration coupled to the implantable lead when the implantable lead is located in or near the heart.
 18. The method of claim 15, wherein the information indicative of the motion of the implantable lead includes information indicative of a blood pressure when the implantable lead is located in or near a blood vessel.
 19. The method of claim 15, wherein the receiving the second signal from the implantable lead includes receiving a voltage indicative of a change in a capacitance provided by the implantable lead; and wherein the extracting information indicative of the motion includes measuring the received voltage.
 20. The method of claim 15, wherein the first signal includes a pulsed signal provided to a first capacitance provided by the lead; and wherein the method includes charging the first capacitance using the pulsed signal; wherein the receiving the information includes receiving a first voltage developed across the first capacitance; and wherein the extracting information indicative of the motion includes comparing the first voltage to a specified first threshold. 